PROJECT SUMMARY The long term goal of the application is to understand how lipopolysaccharide (LPS) is catabolized in the microbial world. In particular, the application focuses on gut microbiota mediated degradation. LPS is a saccharolipid common to nearly all gram negative bacteria. It is composed of a highly acylated di-glucosamine backbone onto which a conserved inner core of sugars is attached. While much is known about remodeling of LPS by the producing organisms, little is known about how LPS is degraded, turned over, and recycled. This is in sharp contrast to other abundant (macro) molecules in bacteria, such as proteins, phospholipids, and nucleic acids, for which opposing biosynthesis and degradation pathways are well established. Often, these pathways occur in the same organism and are tightly regulated to prevent self-damage. LPS is a potentially rich carbon source, yielding highly reduced fatty acids and component carbohydrates that can reenter primary catabolic pathways that can extract energy. Details concerning how LPS is broken down are largely unknown. Knowledge concerning LPS catabolism is potentially important beyond completing a gap in the carbon cycle. LPS, also called endotoxin, is a potent agonist of the innate immunity Toll-like receptor TLR4. There is a growing body of evidence that the gut bacterial microbiome components such as LPS contribute to the pathology of a number of chronic epidemic diseases, including atherosclerosis, non-alcoholic fatty liver disease (NAFLD), insulin resistance, and Type 2 diabetes mellitus. This constellation of metabolic dysfunction, collectively termed metabolic endotoxemias, is at the forefront of public health concerns; nearly 6% of the world?s population lives with diabetes, 15-30% exhibit signs of NAFLD, and cardiovascular disease is the leading cause of morbidity in the western world. Once more, obesity, inflammatory bowel disease, and intestinal microbiome dysbiosis from infection/antibiotics may be a predisposing risk factor for disease development. LPS that crosses the intestinal epithelial barrier can induce low grade systematic inflammation, elevate pro-inflammatory cytokine pools, and stimulate the onset and progression of disease for which inflammation appears to be a common driver. We propose intralumenal LPS degradation by the microbiota flora can help decrease endotoxin translocation, potentially lowering the inflammatory tone. In return, these commensals are rewarded with a constant and plentiful nutrient source. This proposal seeks to develop and apply a screen to identify LPS degrading activity among bacterial constituents of the gut microbiota. Pilot studies have uncovered novel LPS degrading activity in certain strains, for which the enzymatic source will be identified. Ultimately, this information will be used to test whether shifting towards a more robust intralumenal LPS catabolizing microbiome can translate into a treatment for endotoxemia induced inflammation.